Tribological Evaluation of Few-Layer Nitrogen-Doped Graphene as an Efficient Lubricant Additive on Engine Cylinder Liner: Experiment and Mechanism Investigation

The restricted adsorption capacity of ordinary graphene at high temperature limits its application in engine lubrication. To address this, nitrogen-doped element-modified graphene with strong adsorption and superior lubricating properties is prepared by a bottom-up chemical strategy in this study. The reciprocating tribometer is aimed at simulating the piston operating environment to determine the lubrication performance of nitrogen-doped graphene. The characterization and analysis of the wear marks are performed by means of depth-of-field microscope, scanning electron microscope, energy dispersive spectrometer, and other instruments. The experimental data demonstrate that the friction-reduction and anti-wear properties of PAO 6 base oil are enhanced by 22.4% and 56.9% (100 °C), respectively, after the addition of 0.4 wt% nitrogen-doped graphene. Besides, the abrasive and adhesive wear are significantly reduced, which are attributed to its inter-layer slip along the sliding direction and superior adsorption performance. Finally, the interfacial lubrication mechanism of lubricant protective film under high-temperature conditions is revealed.